Image forming method and image recording device for performing this method

Abstract: An image forming method in which digital image data are stored in a memory and are read out of the memory to form images on copy sheets in a first image orientation or in a second image orientation rotated through 180° with respect to the first image orientation. First image data relating to images to be formed in the first orientation are stored in the memory in ascending address sequence, starting from the first free memory address. Second image data relating to images to be formed in the second orientation, however, are stored in the memory in descending address sequence, starting from the last free memory address, while reading out from the memory is effected in ascending address sequence for both the first and the second image data. The available memory space is thus used without any capacity loss and hence extremely efficiently, because both the first and the second image data are stored in contiguous relationship and hence the memory space still available remains contiguous.

Description: The invention relates to an image-forming method in which digital image data representing image information from one or more documents, are stored in a memory and are read out of the memory to form images on copy sheets in a first image orientation or in a second image orientation rotated through 180° with respect to the first orientation, first image data which relate to images to be formed on copy sheets in the first image orientation being stored in the memory in ascending address sequence, second image data which relate to images to be formed on copy sheets in the second image orientation being stored in the memory in descending address sequence, and reading out from the memory taking place in ascending address sequence for both the first and the second image data. The invention also relates to an image recording device for performing this image forming method. A method of this kind is known from US-A-4 453 841, in which copy sheets can be provided with an image on the front and back. In these conditions, when processing copy sheets so transported through the image forming device that the longest peripheral side extends in the direction of transport, it is necessary that the image data for the front or back should be rotated through 180° to ensure that the orientation of the image information is the same on the front and back of the sheet. This is effected by reading out of the memory in the reverse sequence the image data for that side of a copy sheet whose image data have to be rotated through 180° or storing the same in the memory already in the reverse sequence. The latter option is the most attractive because in that way reading out of the memory for image forming purposes can always take place in the same direction irrespective of the orientation. However, in storing image data which are to be stored in the memory in the reverse sequence there is the problem that it is not possible efficiently to use the available memory space. Since it is impossible to know beforehand how much memory space such image data are to occupy, certainly if the image data are also to undergo compression, the option chosen is to reserve a predetermined memory space which is ample enough on the basis of the least favourable situation in respect of data compression. The object of the invention is to provide an image forming method in accordance with the preamble in which effective use is made of the available memory space. This object is achieved in that the first image data are stored in the memory starting from the first free memory address and the second image data are stored in the memory starting from the last free memory address. As a result, there is no need to reserve any predetermined memory space for the image data required to be stored in reverse sequence in the memory. In this way, the available memory space is used without any capacity loss, and hence extremely effectively, because the image data which do not require to be rotated are stored in the memory from the first free memory address from front to back and the image data required to be rotated are stored in the memory from the last free memory address from back to front. The invention is directed to an image-forming method and to an image recording device as set out in claims 1 and 2. The invention will be explained in detail with reference to the following description and accompanying drawings wherein: Fig. 1 is a diagram showing an image recording device using the method according to the invention, and Fig. 2 diagrammatically illustrates part of an image processing device for performing the method according to the invention. The image recording device shown in Fig. 1 comprises a scanning device 1 and a printing device 2. The scanning device 1 is provided with a tubular lamp 5, a reflector 6 co-operating therewith, and by means of which a narrow strip of a document 8 on a platen 7 is exposed, and an array 10 of imaging glass fibres (a "Selfoc" lens array), by means of which the light reflected image-wise by the document is projected on to a sensor array, e.g. in the form of a CCD array 12. The scanning device 1 is advanced by drive means known per se (not shown) in the direction of arrow 13 at uniform speed so that the document 8 is scanned line-wise by the CCD array 12. In this way each image dot on the document is converted to an analog signal corresponding to the grey value of that image dot. The analog signal is then converted by an A/D converter to an 8-bit digital signal for each image dot whereupon the digital signals (image data) are fed to an image processing device 15 via a number of parallel lines of a data bus 14. In the image processing device 15 the image data, often in compressed form, are stored in a memory and are subjected to one or more known image processing operations (thresholding, dithering, histogramming, enlargement, reduction, rotations etc. ) The image data processed in this way are then returned to the memory or placed in another memory and then, possibly after decompression, fed to the printing device 2 via a data bus 16. The printing device 2 is provided with an endless photoconductive belt 20 which is advanced at uniform speed in the direction of arrow 24 by drive or guide rollers 21, 22 and 23 respectively. An LED array 25 is so controlled by means of the processed image data fed via data bus 16 that the photoconductive belt 20 after electrostatic charging via a corona device 30 is exposed image-wise line by line. The latent charge image formed on the belt 20 as a result of the exposure is developed with toner powder by means of a magnetic brush device 31 to give a toner image which in a first transfer zone is then brought into contact under pressure with an endless intermediate belt 32 made of or covered with a resilient and heat-resistant material, e.g. silicone rubber. In these conditions the toner image is transferred by adhesive forces from the belt 20 to the belt 32. After this image transfer, any toner powder residues remaining are removed from the photoconductive belt 20 by a cleaning device 33, so that the belt 20 is ready for re-use. The intermediate belt 32 is trained about drive and guide rollers 34, 35, the intermediate belt 32 being heated to a temperature above the softening temperature of the toner powder, e.g. by an infrared radiator disposed inside roller 35. While the belt 32 with the toner image thereon is being advanced, the toner image becomes tacky as a result of the heating. In a second transfer zone between the belt 32 and a pressure roller 36, the tacky toner image is transferred under the influence of pressure onto and simultaneously fixed to a copy sheet fed from one of the reservoirs 37 or 38. The copy obtained in this way can finally be deposited in a receiving tray 39 or be fed by a deflector element 40 (disposed in the position indicated by broken lines), to a turn-over device 41. The copy sheet is turned over in device 41, and is then re-fed to the second transfer zone between the belt 32 and the pressure roller 36 in order to be printed with a powder image on the other side in said transfer zone and then deposited in the tray 39. Fig. 1 shows only two copy sheet reservoirs 37 and 38 but of course the number of reservoirs can be extended to accommodate different sheet formats (e.g. A5, A4 and A3 and also other e.g. American, formats). In addition, it is necessary to be able to feed the various copy sheet formats in different orientations - namely longitudinal feed (with the longest peripheral side in the direction of transport) or transverse feed (with the shortest peripheral side in the direction of transport) so that copies of one and the same copy sheet format can be produced with the orientation of the image information situated optionally in the direction of transport of the copy sheets through the image recording device or at right angles thereto. Although it is obvious to process copy sheets in the transverse feed orientation from the aspect of the production speed of the image recording device, and it is almost usual to provide the image information thereon in the same orientation, there are applications in which a different orientation of the copy sheets and/or the image information is selected. On the one hand, copy sheets whose longest peripheral side dimension is larger than the working width of the image recording device can be processed only in the longitudinal feed orientation, in which case the image orientation is usually also required in the direction of transit. On the other hand, orientation of the image information in the direction of copy sheet transit is required in the application in which two blocks of image information (two original pages) are to be imaged next to one another on a copy sheet in the transverse feed orientation (e.g. two A5 format images on an A4 copy sheet). A number of copies formed in this way is folded between the blocks of image information, for example, after being deposited, and may if required be stapled in order thus to form a booklet. In the processing of image information with an orientation in the direction of transit to form copies printed on both sides, however, there is the problem that the turning over of the sheet in the turn-over device 41 causes the image information on the back of the copies to be rotated through 180° with respect to the image information on the front, and of course this is unacceptable. One solution to this problem comprises feeding the image data from either the front or back of the document 8 rotated through 180° from the image processing device 15 to the printing device 25. For this purpose, 180° rotation of said image data is carried out in the image processing device 15 in a manner to be described hereinafter with reference to Fig. 2. Fig. 2 shows that part of the image processing device 15 by means of which the 180° rotation of the image data can be effected by two consecutive reflections of the image data, such reflections being carried out with respect to axes at right angles to one another. The digital signals for each image dot are fed via a data line 50 to a compression device 51 in which the image data for each scanned line of the document 8 are compressed in a manner known in the art. The compressed data are then stored in a memory 52. The image data of all the documents required for a specific copy job are then stored line by line in said memory 52. In these conditions, the image data of those documents which do not need to be rotated are stored in the memory directly from the compression device 51, in ascending address sequence starting from the first memory address. The beginning and end addresses inter alia of each document stored in the memory and the addresses of the freely available memory space are registered in the central control unit 55 of the image recording device shown diagrammatically in Fig. 2. The image data of those documents which are to be rotated through 180° are placed in the memory 52 in a different way in order that the first of the two reflections required can be carried out in this way in combination with reading out of the memory 52 in the correct sequence. The image data of these documents are fed to the memory 52 line by line from the compression device 51 and stored therein in descending address sequence starting from the last free memory address. In order that the first reflection of the image data can then be carried out during the reading out of the memory 52 in ascending address sequence, the compressed image data must be reversed, in respect of each scanned line of the document 8, in sequence within each line, before said data are stored in the memory 52. This reversion of the image data for each line is carried out in a LIFO line memory 53. The operation of the LIFO line memory (LIFO = Last-In-First-Out) is such that of the digital signals of one line fed serially to said line memory 53 the last signal fed to said memory 53 is the first to be outputted and vice versa. The above-described method provides optimal use of the memory 52 because, on the one hand, those image data which do not have to be rotated are stored in the memory in contiguous relationship in ascending address sequence from the first free memory address while on the other hand the image data which are required to be rotated through 180° are stored in contiguous relationship in descending address sequence from the last free memory address. As a result, the memory space still available is also contiguous and hence available for optimal use. In this way it is possible also for all the image data stored in the memory to be read out therefrom in the same direction, i.e. in ascending address sequence. After a set of documents of a copying job or part of said set has been stored in the memory 52 in the manner described above, the various process functions of the printing device 2 can be controlled by the central control device 55. In these conditions the central control device 55 also controls the reading out of the image data from the memory 52 in the document sequence programmed for a specific copying job. As already stated, the image data are read out of the memory 52 in ascending address sequence, the image data of one line being fed each time to a decompression device 56 to be decompressed therein in a manner known from the art. With regard to those documents whose image data must be rotated through 180°, this read-out method has the effect that the first reflection (of image lines within the document) is carried out in this way. After the processing of the image data by the decompression device 56, the image data are subjected to other known image processing operations via a data bus 60 for each image line and finally fed to the LED array 25 of the printing device 2. The second reflection of the image data (image dots within each image line) by means of which the intended 180° rotation is completed, is effected by means of. a LIFO line memory 57 which in similar manner to the above-described LIFO line memory 53 reverses the sequence of the image dots within a line. The data of those documents which do not undergo rotation are fed directly from the decompression device 56 to the data bus 60. The above description assumes that it is already known which documents will require 180° rotation of the image data to effect the correct orientation of the image information when the copying job for the image-recording device is programmed. However, there may be cases in which, just after the set of documents has been scanned by the scanning device 1 and the image data have been stored in the memory 52, it is found that the image data has to be rotated through 180° in respect of one or more documents. In that case the associated image data are read out from the memory 52 and again fed to the image rotation operation via a data bus 61 (see Fig. 2). In these conditions such data are placed in the memory 52 directly in descending address sequence via the decompression device 56 and the compression device 51 (and hence not via the LIFO line memory 53), whereby the first reflection (of the image lines within the document) is effected because reading out from the memory 52 always takes place in ascending address sequence. The second reflection (of image dots within each image line) is then carried out, while reading out the associated data, by reversing in sequence such data within an image line by means of a LIFO line memory 57 for each image line, and then feeding the data to the data bus 60. In the above-mentioned situation in which rotation through 180° is required subsequently, it may occur that decompression and compression of the image data during the rotation process results in a different compression factor of a document. This may give rise to problems if the compression factor during this subsequent rotation is reduced and thus more memory space is required in the memory 52 than before the rotation process. To obviate such problems, in this situation the compression technique applied is adapted in manner known per se. In addition, it is attractive to sort the documents from the central control device 55 in a manner known from the art in respect of the quantity of image data (difference between beginning and end addresses of such image data) for each document and, during the subsequent rotation, start with the document having the largest quantity of image data and then reading the other documents successively out of the memory 52 in sequence of descending quantity of image data and again storing them in the memory 52. In this way image data can be prevented from being spread over a number of locations in the memory 52 during this rotation. The control of the image processing components of Fig. 2 and hence the control of the data streams according to the invention, is effected in manner known per se from the central control device 55 and is shown diagrammatically by broken lines in Fig. 2. Although 180° rotation of the image data is described above as a solution to problems which may occur in respect of image orientation in the direction of transit in combination with processing to copies printed on both sides, there are other applications in which use can be made of the possibilities offered by rotation as shown in Fig. 2. One such application, for example, is making booklets by printing two blocks of image information next to one another on a copy sheet such blocks being disposed at 180° rotation relatively to one another, and folding such a copy sheet between the two blocks of image information. In another application, the 180° rotation can be used to ensure, independently of the positioning of the document 8 on the platen 7 (top of the image on the document 8 at the front or rear of the image recording device) that the top of the image on the copy is always situated at the front or the rear of the image recording device in order to create a clear situation for the finishing (e.g. stapling) of the copies. In addition there are specific applications possible for the rotation according to Fig. 2, in which it is not the complete 180° rotation which is applied, but only one of the two reflections of the image data making up the 180° rotation.

Claims: An image-forming method in which digital image data representing image information from one or more documents, are stored in a memory and are read out of the memory to form images on copy sheets in a first image orientation or in a second image orientation rotated through 180° with respect to the first orientation, first image data which relate to images to be formed on copy sheets in the first image orientation being stored in the memory in ascending address sequence, second image data which relate to images to be formed on copy sheets in the second image orientation being stored in the memory in descending address sequence, and reading out from the memory taking place in ascending address sequence for both the first and the second image data, characterised in that, the first image data are stored in the memory starting from the first free memory address and the second image data are stored in the memory starting from the last free memory address. An image recording device for performing the image forming method according to claim 1, comprising means for generating digital image data representing image information from one or more documents, a memory (52) for the storage of image data, an image forming device (2) by means of which images can be formed on copy sheets in a first image orientation or in a second image orientation rotated through 180° with respect to the first image orientation, and control means (55) which so control the memory (52) that first image data relating to images to be formed on copy sheets in the first image orientation are stored in the memory (52) in ascending address sequence starting from the first free memory address, that second image data relating to images to be formed on copy sheets in the second image orientation are stored in the memory in descending address sequence starting from the last free memory address, and that the memory (52) is read out in ascending address sequence for both the first and the second image data for the purpose of controlling the image forming device (2).

Inventors: KESSELS GERARDUS GERTRUDA JOHA, VAN VLIEMBERGEN EDUARDUS JOSEP, KESSELS, GERARDUS GERTRUDA JOHANNES CATHARINA, VAN VLIEMBERGEN, EDUARDUS JOSEPHUS WILLIBRORDUS
Applicants: OCE TECH BV, OCE-TECHNOLOGIES B.V.
Application year: 1994
Main classification: G06T1
IPC codes: H04N1, G06K15